The present invention relates generally to void-maintaining geosynthetic systems for the drainage of water and other fluids, and more particularly to geosynthetic structures having a void-maintaining core that may be sandwiched between attached or uni-formed geotextile layers. Geosynthetic structures of the invention are ideal for providing subsurface drainage for roadways and other large structures such as parking lots, retaining walls and buildings.
The building of large structures such as roadways, buildings, parking lots, retaining walls, embankments and the like often involves the excavation, re-contouring and other movement of large quantities of earthen materials such as soil, rock, earth, gravel, sand and the like. Most large structures have underlying foundations of some sort to support the weight of the structure and thereby stabilize the structure in its desired position with respect to the earth and with respect to other parts of the same structure. For example, roadways and parking lots usually have foundations comprising a base aggregate immediately under the paved surface, and a subgrade layer under the base aggregate which supports the weight of both of the overlying structures. Commonly, both the base and subgrade are formed of stones, soil and other earthen materials and subjected repeatedly to grading, tamping or other compaction operations and thereby formed into a foundation of desired density, elevation, inclination and direction. Buildings commonly have concrete foundations or concrete slabs that support the weight of the overlying structure.
The presence of water or other fluids near, within or under such foundations can be quite disadvantageous. For example, water or other fluids in the foundation materials underlying such structures can cause hydraulic pore pressure buildup and reduction in the effective stress in the soil materials. These conditions can directly or indirectly contribute to failure of the underlying materials that support the overlying foundation and can thereby also cause a failure of the overlying structure. It is thus important to positively control the water or other fluids and dissipate pore pressure underlying large structures and in the vicinity of and underlying the foundations of such large structures.
The movement of soil particles around and underlying structures is not limited to that caused by the presence of fluids. Movement can occur from repeated or repetitive dynamic loads, as well as static loads that cause destabilizing stresses within the soil structure. One way of controlling such movement is to provide reinforcing products such as frameworks which are integral to the materials underlying the foundation, or within it, to thereby prevent or impede such undesired movement. Geosynthetics are materials often used to provide such a framework. The use of geosynthetics contributes to controlling movement of soil particles and structural fill materials in four primary ways:
1) By creating higher degrees of friction between the natural materials and the surface of the geosynthetic when compared to the frictional characteristics of the soil itself in order to minimize soil movement in horizontal, vertical and diagonal directions.
2) By confining soil fill material within the geosynthetic structure in an attempt to control lateral movement of soil particles.
3) By providing a nonporous, impermeable membrane type barrier that minimizes vertical migration of soil particles and fluids. At times, horizontal and diagonal movement of soil particles is impeded by roughening or texturing the geosynthetic in order to increase the friction between the soil and the geosynthetic.
4) By providing a semiporous, porous, or permeable barrier that minimizes vertical migration of soil particles by not allowing soil particles to move through openings in the geosynthetic that are effectively smaller than the diameter of the soil particles themselves, while also allowing fluids to migrate vertically, diagonally and horizontally irrespective of gravity through one or more layers of a single or multi-ply geosynthetic.
These porous, semiporporous or permeable geosynthetics allow fluids to pass vertically and horizontally through their structures. Capillary connections sometimes occur and are one aspect that allow fluids to migrate vertically and diagonally irrespective of gravity through multi-ply geosynthetics. Capillary connections are created by the contacting of two or more plys of geosynthetics and provide continuous vertical or diagonal capillary paths through which fluids may travel. Typically, capillary connections may appear in a semi-continuous pattern across the horizontal plane of a geosynthetic comprising more than one ply. These connections, which are formed when the polymer strands of one ply of a geosynthetic contact the polymer strands of another ply often occur when layers of geosynthetics are arranged or constructed to allow one ply to be placed directly on top of another ply. Polymer strands of individual geosynthetic plys assist fluid migration in the horizontal plane of the specific geosynthetic ply. This horizontal transmission of fluid can be expressed as a rate of flow per unit width within the plane of a geosynthetic and is typically called xe2x80x9ctransmissivity.xe2x80x9d On the other hand, the vertical transmission rate of fluid, or xe2x80x9cpermittivityxe2x80x9d of a geosynthetic is typically expressed by measuring the rate of flow per unit area per unit thickness. Permitivity is a quantifiable property that can be controlled during the maufacturering process.
Vertical and diagonal capillary connections can be created even when two or more plys of geosynthetic are arranged in substantially but parallel planes when polymer strands of one ply become in contact with the polymer strands of another ply. This can occur under the normal pressures that are placed upon the geosynthetic from the overlying soil burden which forces polymeric strands of the separate plys together thereby allowing fluids to migrate against gravity at the sites of the continuous capillary connections. The flow of fluids through a geosynthetic against gravity is often referred to as xe2x80x9cwicking,xe2x80x9d and is distinguished from permitivity. Wicking occurs after field installation of the product and is not a predictably quantifiable characteristic of the system but is dependent on a number of different factors. Wicking, the fluid transmission against gravity resulting from capillary connections created by the deformation and intercontact of geosynethic plys, is a property that is sometimes advantageous and other times disadvantageous.For example, in applications where the user desires water to be transmitted against gravity these, capillary connections may provide a benefit. In contrast, using geosynthetics in applications where the user does not want fluid to pass via the mechanism provided by the capillary connection can be a detriment to the particular structure.
In general, geosynthetics are manufactured as substantially planar, or sheetlike, products from polymeric materials. Geosynthetics are usually made in large scale, for example, several meters in width and many meters in length so that they are easily adaptable to large scale construction and landscaping uses. Some geosynthetics are flexible or fabric-like and therefore conform easily to uneven or rolling surfaces. Some geosynthetics are manufactured to be less flexible but to possess great tensile strength and resistance to stretching or great resistance to compression. Certain types of geosynthetic materials are used to reinforce large man-made structures, particularly those made of earthen materials such as gravel, sand and soil. In such uses, one purpose of using the geosynthetic is that of holding the earthen components together by providing a latticework or meshwork whose elements have a high resistence to stretching. By positioning the geosynthetic integral to the gravel, sand and soil, that is, with the gravel, sand and soil within the interstices of the geosynthetic, unwanted movement of the earthen components is minimized or eliminated. Most geosynthetic materials, whether of the latticework type or of the fabric type, allow water to pass through them to some extent and into the material within which the geosynthetic is integrally positioned. Thus, geosynthetic materials and related geotechnical engineering materials are used as integral parts of man-made structures or systems in order to stabilize their salient dimensions.
A particular problem faced by the FHWA, the DOT and many highway and transportation agencies across the United States and elsewhere is the high-cost and difficult maintenance of state and interstate roadways. A significant cause of this high cost and these difficulties is the entrapment and retention of water and other fluids which damage roadways and greatly reduce their useful life. This is the case even on those projects where conventional geosynthetics are used. Water in pavement systems that are inclusive or exclusive of geosynthetic is one of the principal causes of pavement distress. Fluid such as water enters the subsurface either from the subgrade soil, that is, the native ground upon which the roadway is constructed, or from rainwater or floodwater penetrating open spaces such as cracks and pits within the road surface. Under common usage, vehicular traffic across the roadway produces a dynamic or repetitious loading force on the road that creates a xe2x80x9cpumping actionxe2x80x9d that draws fluid through the subgrade into the subbase or base coarse of the road. When this fluid is retained within the subbase or road base, damage to the roadway occurs. As indicated in the AASHTO design methodology (1993), drainage performance can range from excellent (water is removed from the roadway systems within two hours) to poor drainage (water is removed within one month). The corresponding drainage coefficient (direct design parameter) for an excellent drainage is 3.0 times greater then the corresponding drainage coefficient for poor drainage. The higher drainage coefficient increases the structural number. Therefore, the service life of the structures can be extended or the overall structural cross-section can be reduced. When there is a high fluid content within the soil supporting the traffic lanes, reduced bearing capacity can occur, resulting in deformation of the contour of the road, wheel rutting, and premature collapse or failure of the roadway.
Another drainage issue particular to construction of roadways and other large structures in regions with cold climates relates to frost damage to pavements due to frost heaving and subsequent thawing. Frost heaving, the raising of the pavement surface occurs due to the formation of ice lenses, which can grow up to several centimeters in the thickness, in the underlying soil. Differential frost heaving leads to adverse pavement roughness and hazardous driving conditions. Thawing or frozen pavements in frost-melting periods causes a supersaturated soil condition. If the drainage provisions are inadequate, the bearing capacity of the pavement is substantially reduced, which in turn causes bearing capacity failure or surface cracking. Traffic loading during the thaw season can also pump fine-grained subgrade soils into the subbase or base course. Among the economic losses by frost damage are costs of repair and maintenance, possible restrictions of vehicle weight-limits or even complete closure of the traffic. All of these conditions can be extremely costly. To reduce damage caused by frost heaving, in 1963 the U.S. Army Corps of Engineers suggested two strategies: 1)the control of surface deformation resulting from frost action by limiting the amount of frost-susceptible soil subjected to freezing temperatures; and 2) employing designs of adequately large bearing capacities sufficient to withstand stresses experienced during the most critical climatic period. This means a significant increase in aggregate thickness and the concomitant increase in cost and time required to construct a given structure.
Design methods based on the above two concepts call for the use of clean, nonfrost-susceptible base material. Such material is becoming more and more expensive to obtain and transport. Due to the required serviceability that an engineer must account for in the design for their clients, these types of expensive soils are often forced to be considered in civil engineering projects, thus making demand for them higher and, consequently, an increase in their prices.
Frost damage can be reduced by introducing a capillary break, or water barrier, to reduce water migration into the freezing front. Various methods are known to deal with this problem. For example, Finland and Sweden have used a layer or sand to break the capillary connection between frost-susceptible soils (Rengmark, 1963; Taivenen, 1963). This insulating layer of sand was found to help reduce and smooth frost heave, and also to increase the bearing capacity during the spring thaw.
Before the present invention, previous drainage systems using geosynthetic structures are exclusively limited to providing drainage at the edge or shoulder of a roadway. These edge-drain systems are commonly located within a covered trench originally dug along the shoulder of the roadway, in an area which receives little or no dynamic load from the roadway. Usually serving a dual purpose, the edge-drain relies upon natural drainage from directly beneath the road surface within the subbase or subgrade to carry fluid to the edge-drains for collection and further distribution, for example, by way of a shoulder pipe. The material of the subbase or subgrade acts also as a filter to prevent adjacent soil from clogging the drainage system. The drainage system directly beneath the surface of a roadway is often made of unstabilized granular, asphalt stabilized granular, or cement stabilized aggregate material. Such xe2x80x9cnatural materialxe2x80x9d drainage systems, if installed properly, can be used to carry large amounts of fluid from the subbase to the edge-drain.
There are many disadvantages to natural material drainage systems, however. Such systems require the subsurface aggregate to possess a uniform size gradation to provide void spaces, that is, interconnecting holes within the drainable base to carry fluid. Disadvantageously, the requirement for interconnecting void spaces to afford good drainage conflicts with road pavement systems designed for long-term use. This is so because roadways designed for long-term use require minimal void spaces in order to reduce the movement of particles, sand and aggregate. Free-draining aggregate usually require an asphaltic or cement stabilize binder to facilitate construction. Additionally, a well-graded granular or geotextile filter layer is needed to prevent contamination of the open graded base through the migration of subgrade fines. This extra filter layer further increases the cost of the roadway construction. Furthermore, high construction costs are incurred for a complete drainage layer of natural stone or sand that must be installed with precision, and extensive on-site quality control must be exercised, in order to produce a high-flow draining system which lasts for the life of the overlying paved surface.
When positioned directly beneath the road surface, conventional geosynthetic structures are primarily used to provide reinforcement of the base, subgrade stabilization, subgrade restraint, separation of the base course from the subgrade, or as a thermal break to provide insulation from temperature changes. Until the present invention, however, geosynthetic materials had not been designed or implemented to provide a positive drainage system effective enough to provide adequate drainage for an entire roadway or for an entire roadway portion. Similarly, until the present invention, no geosynthetic material had ever been designed to break the capillary connection that can occur as a result of the repeated dynamic traffic loads that can cause a capillary connection between different plys of geosynthetics, nor has a geosynthetic ever been used to provide a void maintaining system for the entire design life of a roadway and thereby serve as an effective capillary break to prevent moisture migration into the base course layer or into the frost susceptible soil layer, or underneath an entire roadway.
There is therefore a need for a drainage system that can be positioned within a large structure and provide efficient and cost-effective drainage for the structure while also providing a capillary break by utilizing components which can be engineered and manufactured offsite.
The present invention overcomes the previously mentioned disadvantages by providing a drainage system which provides interconnected drainage voids and also functions as a capillary break under substantial portions of the ground underlying roadways, parking lots, retaining walls, buildings and other large structures. Structures of the present invention are unitary void-maintaining geocomposite structures (to be sold under the trademark xe2x80x9cUVMGxe2x80x9d) UVMG""s according to the invention can be constructed and positioned within one or more of the subsurface levels at predetermined locations under a large structure such as a roadway or building. The present UVMG""s typically comprise a void-maintaining core such as a geonet adjacent to one or more layers of fluid-transmissable geotextile fabric. The structures are unitary in that the core element is preferably manufactured simultaneously with its filtration medium to form a unitary geocomposite. Another method of manufacture is for the core element and geotextile elements to be formed separately and then adhered to one another by heat, laser or electron beam welding, or by means of adhesives applied to one or more of the components to thereby form a unitary structure in advance of installation of the UVMG at a desired site.
The permittivity of a material relates to its ability to permit gases, water and other fluids to pass vertically, or substantially vertically, through the material. The fluid-transmissible layers of the present invention provide high permittivity of subsurface fluids such as water into the core element. Geotextiles are preferred as the fluid-transmissible layers of the invention. Other materials possessing high permittivity and high occlusiveness to solids are also suitable for the present invention. Structures of the present invention also possess high transmissivity. The transmissivity of a material relates to its ability to transmit gases, water or other fluids horizontally, or substantially horizontally, in a particular or desired direction. Typically, permittivity is measured as the rate of flow per unit area per unit width while transmissivity is measured in terms of rate of flow per unit width. Core elements of the present invention possess high transmissivity because of their interconnecting openings, which permit fluids to flow substantially horizontally away from the overlying or underlying structure. Thus, UVMG""s eliminate many of the problems presented by the presence or movement of fluids such as water in the areas underlying large structures. By eliminating these problems, the useful life of the subject structure is extended.
The present invention relates generally to unitary void-maintaining geocomposite structures and systems for water drainage, and more particularly to such geocomposite structures combined with additional drainage elements such as pipes, conduits, edge drains, culverts and ditches for the subsurface drainage of roadways and other large structures such as parking lots, retaining walls and buildings.
A principal object of the present UVMG invention is to provide a subsurface drainage system that, among other things, provides a capillary break to thereby prevent unwanted movement of the structure, such as frost heaving, to thereby extend the useful life of a roadway or other large structure.
It is another object of the present invention to provide cost-effective alternatives to previous large-structure subsurface drainage systems.
An additional object of the invention is to provide unitary geocomposite materials which include both void-maintaining elements and geotextile or other filtration elements having high permitivity for fluids while preventing solid particles that are larger than openings in the filtration element from entering the void-maintaining system.
It is a further object of the present invention to transfer certain quality control aspects of road construction and reconstruction from the construction site to a manufacturing facility for roadway drainage products.
It is yet another object of the present invention to provide subsurface drainage unitary void-maintaining geocomposites as part of a greater road subsurface geosysthentic system to thereby enable efficient reinforcement, separation, filtration, gas transmission and egress, and drainage for a large structure such as a roadway, retaining wall, parking lot or building.
In accordance with this and other objects, the present invention provides a drainage system for draining fluids away from a roadway or other large structure, comprising a unitary void-maintaining geocomposite, the geocomposite comprising a geocomposite core element having a plurality of interconnected voids, the core element having an upper surface and a lower surface, and at least one fluid-transmissible layer of high permittivity adjacent the upper surface, wherein the layers are constructed and arranged so that the geocomposite maintains voids of sufficient dimension that the water from the roadway or other large structure can move freely through the geocomposite, and wherein the geocomposite is sloped downwardly from the roadway or other large structure.
The unitary void maintaining geocomposite may further comprise at least one fluid-transmissible layer, for example, a geotextile, adjacent the lower surface of the void-maintaining geocomposite, and may also further comprise drain means adjacent the void-maintaining geocomposite and communicating therewith such that the fluid can move from the void-maintaining geocomposite to the drain means, wherein the drain means is sloped preferably downwardly from the void-maintaining geocomposite. In accordance with advantageous drainage aspects of the invention the void-maintaining geocomposite is sloped downwardly away from a portion of the roadway or the large structure such that the fluid is directed away from the roadway or the large structure and the void-maintaining geocomposite communicates with the drain means under the roadway or at a margin of the roadway or the large structure.
In accordance with additional objects of the invention, the drain means may further comprise a ditch or culvert adjacent a margin of the roadway or the large structure, and the drainage means may comprise perforated piping such as is commonly found in civil engineering applications.
In some preferred embodiments of the present invention, the void-maintaining geocomposite wraps around the circumference of the perforated piping and the perforated piping is connected to further drains means wherein the further drain means is one or more selected from the group consisting of non-perforated pipes, drainage ditches, sumps, canals, streams and rivers. Preferably one or both of the geotextile layers are attached to the geocomposite core element by heat or fusion welding, by laser welding, or by adhesives known in the geotextile arts. Of course, as one of skill in the art can appreciate, in certain applications, it may be most efficacious to position the geotextile layers adjacent the geocomposite core element without attaching them to one another. This may be preferable in situations where separate portions of geocomposite core element are overlapped or butt joined to one another and where it is desirable that no similar joint exists in the corresponding geotextile layer.
In other preferred embodiments of the invention the geocomposite core element comprises a geonet such as that found in U.S. Pat. No. 5,891,549 to Beretta et al. In other preferred embodiments, the geocomposite core element is tri-planar such as shown in U.S. Pat. No. 5,255,998 and comprises polyethlene, polypropylene or other polymer derivatives, and both fluid-transmissible layers are geotextiles that are nonwoven and needle punched. U.S. Pat. Nos. 5,891,549 and 5,255,998 are incorporated herein by reference.
In accordance with additional advantageous aspects of the invention, the void-maintaining geocomposite structure is constructed and arranged to form a wrapping adjacent to and around the circumference of the perforated piping such that a portion of one of the upper or lower fluid-transmissible geotextile layers is removed along the length of the wrapping so that the geocomposite core contacts the piping and the removed portion of the one of the upper or lower fluid-transmissible geotextile layers is overlapping and connected to the other surface fluid-transmissible geotextile layer. As one of skill in the art will recognize, it is advantageous to provide piping or other drain means which has a capacity to carry away a sufficient volume of fluid collected through the relatively large surface area of the present geocomposite core element.
Moreover, by interconnecting the various portions of the present invention such that the various interconnecting voids maintain flow paths for fluid such as water entering the system, large areas under highways, buildings, parking lots, and other large structures can be effectively drained without the necessity of complex and expensive structures. In order to maintain the interconnections preferred in the present invention, the overlapping portions of the fluid-transmissible geotextile layers are connected by ties, welding or by sewing, and the portions of the fluid-transmissible geotextile layers and the geocomposite core element of the void-maintaining geocomposite are held adjacent to the piping by circumferential ties around the geocomposite. Of course, as one of skill will recognize, the present invention is particularly advantageous for draining water-containing fluids or other geologic fluids such as petroleum or natural gas from roadways and other large structures.
In accordance with other aspects of the present invention, a drainage system disposed at a level below the top surface of a roadway for draining fluids such as water away from the roadway is provided, wherein the system comprises a unitary void-maintaining geocomposite comprising a geocomposite core element having a plurality of interconnected voids, the core element having an upper surface and a lower surface, and at least one fluid-transmissible geotextile layer of high permittivity attached adjacent the upper surface, wherein the layers are constructed and arranged so that the unitary void-maintaining geocomposite structure maintains voids of sufficient dimension that the water from the roadway can move freely through the geocomposite, and wherein the geocomposite is sloped downwardly from the top surface of the roadway.
Unitary void maintaining composites further comprise at least one fluid-transmissible layer, preferably a geotextile, attached adjacent the lower surface of the core element and, preferably, drain means adjacent the geocomposites and communicating therewith such that the fluid can move from the geocomposites to the drain means, wherein the drain means is sloped downwardly from the geocomposites such that the fluid is directed away from the roadway, wherein the geocomposite is constructed and arranged to provide a capillary break between the roadway pavement system and the earthen materials under the geocomposite.
In accordance with still other aspects of the present invention, the unitary void-maintaining geocomposites of the present invention can be positioned in a roadway to maximize their effectiveness. For example, in order to provide positive drainage functions, as needed, the geocomposite can be positioned intermittently or continuously below the top Portland Cement Concrete (xe2x80x9cPCCxe2x80x9d) or asphalt layer of the roadway. To provide a capillary break in frost-prone regions, the geocomposite can be placed between the underground water table and frost-penetration depth, or freezing front. The present geocomposites can also be used to provide a capillary break function in non-frost-prone regions where the base layer contains fine grained soil with the potential for vented moisture migration through capillary rising. In order to maximize other advantages of the present invention, the void-maintaining geocomposites may be positioned in multiple layers, and at various levels below the roadway surface in order to maximize drainage efficiency as desired.
The void-maintaining geocomposites of the present invention can be made in large pieces, for example, in pieces several meters wide and many meters long. For convenience and installation, however, the geocomposites of the present invention, or their components can be installed in portions which are interconnected such that the interconnecting voids are of sufficient dimension that the water from the roadway can move freely through the geocomposite and can be connected to drain means such as a ditch or culvert adjacent a margin of the roadway or the large structure or perforated piping.
Moreover, the void-maintaining geocomposites of the present invention can be constructed and arranged to prevent wicking upward, to provide continuous or discontinuous capillary breaks across the area of the geocomposite, or to prevent wicking substantially altogether by the provision of void spaces.
Other advantages of the present invention are found in the methods which it provides. The present invention includes methods for providing drainage systems for roadways or other large structures. For example, the present invention provides a method for constructing a drainage system for draining fluids away from a roadway or other large structure, the method comprising providing a void-maintaining geocomposite including at least one geocomposite core element having a plurality of interconnected voids, the core element having an upper surface and a lower surface, and at least one fluid-transmissible geotextile layer adjacent the upper surface, wherein the components are constructed and arranged so that the geocomposite maintains voids of sufficient dimension that the water from the roadway or other large structure can move freely through the geocomposite, and wherein the geocomposite is sloped downwardly from the roadway or other large structure.
Preferably, the void-maintaining geocomposite further comprises at least one fluid-transmissible geotextile layer of high transmissivity adjacent the lower surface of the geocomposite and drain means adjacent the geocomposite and communicating therewith such that the fluid can move from the geocomposite to the drain means, wherein the drain means is sloped downwardly from geocomposite.
The high transmissivity layers and core elements of the void-maintaining geocomposites of the invention can be positioned at junctions between pieces such that high transmissivity between the void spaces maintained within the geocomposite and those of the drain means is maintained. With respect to the joining of large pieces of the geocomposites, this can be accomplished, for example, by providing geotextile layers which extend beyond the margins of the core composite layer, or by positioning additional pieces of geotextile over the joint areas. With respect to the junctions between the drain means and the geocomposites, portions of the geotextiles can be positioned around the drain means to thereby decrease the likelihood of the intrusion of clogging materials and to maintain the connection between voids of the geocomposites and those of the drain means.
The means and methods of the present invention include the positioning of the geocomposites and drain means in many permutations depending on the particular needs of the structure to be drained. For example, geocomposites of the invention can be positioned below the roadway or large structure and above an aggregate layer if desired. Moreover, the present methods include combinations wherein the geocomposite is positioned below the roadway or large structure in portions which are interconnected such that the interconnecting voids are of sufficient dimension that the water from the roadway can move freely through the connecting portions and thereby through the geocomposite. The present methods include wherein the drain means further comprises a ditch or culvert adjacent a margin of the roadway or the large structure.
As a further advantage, the combinations and methods of the invention comprise wherein the roadway base course comprises materials which have been excavated from the subgrade of the roadway and wherein the roadway base course comprises materials which have been excavated from the subgrade of the roadway and mixed with imported materials.